1. Technical Field
This invention relates to surface treatments of printed media to improve adhesion of laminates and binding adhesives to improve the performance of finishing operations.
2. Description of the Related Art
In an electrostatographic process, a system is used whereby a uniform electrostatic charge is placed upon a reusable photoconductive surface. The charged photoconductive surface is then exposed to a light image of an original and the charge is selectively dissipated to form a latent electrostatic image of the original on the photoreceptor. The latent image is developed by depositing toner, finely divided marking and charged particles, on the photoreceptor surface. Toner becomes electrostatically attached to charged areas of the latent electrostatic image creating a toned developed image that is then transferred from the photoreceptor to a final image support material, such as, for example, paper. The toner is than fixed or fused to the image support material by a process of fusing.
During fusing, heat and pressure may be applied to the toned developed image to cause the thermal fusing of toner particles onto a support material. Pressure may be applied through several methods known in the art that generally include the passage of the toned developed image through a nip formed between a roll pair, plates, and/or belt members maintained in pressure contact. Heat may be concurrently applied to the toned developed image with the application of pressure in the nip, allowing the fusion of the toner image to the support media. The time required for the toner to become fused to the support material, or contact time, may vary depending on image, the type of support material, and the type of toner applied. Balancing the pressure, heat, and contact time may he an important aspect of the fusing process, and these parameters may be adjusted to suit particular machines, process conditions, and printing substrates.
Following the fusion process, the image support material must be released from the fuser, and the fuser must be cleaned of residual toner. This may be accomplished by mechanical means or by coating the surface of the fuser member with a polymer coating and, in some cases, one or more release agent to prevent the toner and/or support material from becoming inappropriately attached to the fuser member. Polymer coatings for a fuser member are well known in the art and include, for example, silicone rubber, fluoropolymers or fluoroelastomers such as polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA-TEFLON™), fluorinated ethylenepropylene copolymer (FEP), polyvinyl fluoride (PVF), and the like and mixtures thereof. On top of this polymer coating, a thin film of one or more release agents may be applied to a fuser member. Release agents are well known in the art and may generally be described as having a polymer backbone that may sterically block contact of the toner with the fuser surface with functional groups attached to the polymer backbone that may bind the release agent to the polymer coating of the fuser member and/or block contact of the toner with the fuser member surface. Common release agents may include, for example, polyorgano-siloxanes, modified polyorgano-siloxanes, polyorgano-siloxane oils and the like, and the use of these polymers to form a thermally stable, renewable self-cleaning layer having good release properties for many toners has been described, for example, in U.S. Pat. No. 4,029,827. Common functional groups useful in release agents include, but are not limited to, mercapto, amino, carboxy, hydroxy, epoxy, isocyanate, thioether, or combinations thereof, and the linkage formed between these groups and the polymer coating of the fuser member may be ionic or covalent in nature. Release agents are described in U.S. Pat. Nos. 4,029,827; 4,101,686; 4,185,140; 5,157,445; 5,395,725; 5,512,409; 5,516,361; 5,531,813; 5,698,320; 5,716,747; 5,747,212; and 6,183,929.
In many fusing applications, adequate coverage of the fuser member surface with a release agent is required to meet the demanding environmental conditions of the printing machine. For example, the release agent must withstand exposure to toner materials and additives, rapid thermal cycling, support media of various compositions and weights, various types of printing, and the like. Therefore, it may be necessary to utilize a release agent that robustly binds to the fuser member under these working conditions and/or to continually reapply the release agent to the fuser member to prevent release agent failure rendering the image quality poor or the fuser member unusable. In either case, the cost for operating the printing machine is dramatically increased.
The characteristics of release agent failure are well known in the art and include, but are not limited to “stripping failure,” defined as a failure of the support medium leaving the exit nip to release from the surface of the fuser resulting in the support medium following the fuser through another cycle jamming the fuser member; “offset” characterized as the gradual build-up of un-transferred or unreleased residual toner on the fuser member allowing toner to be transferred onto the support media in subsequent copying cycles leading to increased background and/or the build-up of release agent on the fuser over the lifetime of the fuser member or other parts of the machine causing interference of the copying process and/or noticeable print quality defects; and “shot offset,” which occurs when the temperature of the toner is raised to a point where the toner particles liquefy, and a portion of molten toner remains on the fuser member. Release properties may be determined by the hot offset temperature since as the temperature nears the hot offset temperature, the likelihood of toner offset occurring increases; and “wavy gloss” characterized as variation of the gloss level within a single imaged sheet caused by a build-up of release agent on the fuser member.
Coupled with the need for release agents that are durable and provide sufficient wetting of the fuser member, it is also important that the release agent have little or no interaction with support material. Unfortunately, residual release agent often remains on the printed support materials and can interfere with the binding of adhesives, laminates, or other binding materials and/or further processing of the printed material, such as, for example, imprinting. Accordingly, we have determined that materials and methods are required that may remove some or all of the residual release agent from the printed material without disturbing the fused toner image.